can you use syphon effect to connect two wells?

I have a 25' shallow 30"id cement-cased dug well that produces 4-5gpm with a soon-to-be installed small submersible pump. I'd like an additional 3-4 gpm without any additional pump.

So my tentative plan is to jet down a 1 1/4" pvc well, then connect this new well with a 1/2" or 3/8" pvc pipe to the old larger well. The idea being that the water level difference between the wells as i draw down the water in the larger well will allow the water to siphon from the small well to the large well.

My water table is about 10 ft down, so the water would need to travel up and then down 10ft +/- a few feet plus, of course, the horizontal distance from the two wells. I could trench several feet from well to well so I might be able to get the vertical drop/fall to more like 7ft. Obviously, I'd need to prime the siphon pipe.

Is this possible do you think? and if it is, any ideas on issues I'm overlooking?

In theory it should work; should be cheap enough to try. The health department might frown if they found out, as around here that would be a "cross connection". You may find, if you do a good job with the pvc (ie...install the right screen in the right place, and develop it correctly)..you'll get way more water than the dug well. I'm a mud rotatry driller, and more as an experiment, I've been installing some replacement shallow wells. I drill, screen, and grout the well just like it was a normal deep well in inconsolidated formations....but just do it in the shallow well aquifer. That's anywhere from 20-50' here. In every case, I've gotten at least 3 times the sustainable flow as the adjacent dug well.

The biggest reason I want to use the cement-cased well is it's big enough for me to install a 1/3hp submersible pump, so I can significantly reduce the cost of running my open loop geothermal system. It's currently running off my deep well 1 1/2 hp pump with 250 ft static water level.

Secondly, if I can get enough water flow, I could use some additional irrigation water for a sprinkler addition.

I've called around to at least 10 well drillers in my area and they all quote me roughly the same cost to do a 25 ft 4" well, as a 600ft typical one they do. Seems crazy to me, but I'm sure they have their reasons.

Well yeah there is good reason why the costs are similar, when you have made an investment of several hundred thousand dollars you need to maximize your return. Drilling 25' wells isn't going to do that.

I assume you are using a bit of hyperbole when you say a 25' well costs the same as a 600' one. That would only be true if they could drill either well in a single day, which is not likely for the deep one.

I don't remember the exact specifics, but the price was the same as the local deep wells which run from 450' to 750', with 600' about average. I understand the large capital costs, and the need to keep those rigs busy. I wasn't complaining--was just surprised at the time.

Anyway, I ran some numbers through a piping software and got the following results with 100' of pvc pipe (50' horizontal + 25' up/down) + fittings.

So what's the largest pipe I can fit in a 1 1/4 pvc casing? How about a 1 1/2"?

Also, thanks hj -- that's a good thought to run the siphon piping several feet deeper (a couple feet below the pump inlet) to prevent breaking the siphon.

Mud drilling is a lot different than rock drilling....600' well is 2-3 days, and that's fast. I would guess the high price is because they don't want to do it...probably because they don't think it will work, or are rock drillers and don't know much about installing a screened well. I charge $2500 for a 4.5" well to the first confining clay....ususally less than 50'. I can do it and clean up and leave in 2-3 hours. Pump system is extra.

I would try to install at least a 2" well.....look online at something called a borezit.....I haven't tried to drill a well with it, but I've used it to bore under driveways and sidewalks lots of times. They say you can install a 4" well with it.